Under certain conditions, the in vivo contact of a transplantable mouse tumor with antibody made in response to the tumor tissue results in the enhanced growth instead of increased immunity to the grafted tissue. This phenomenon is defined as immunological enhancement. The overall objectives of this proposed project are to gain a better understanding of the cellular basis of immunological enhancement and to determine how to manipulate the immune response such that immunological enhancement will prevail under one set of conditions and immunological rejection of allogeneic tissues in another set of conditions. The specific questions we are seeking to answer are: 1) What classes of antibodies are involved in the induction of immunological enhancement? 2) Is the function of the antibody involved in immunological enhancement to release an antigen and/or inhibitor of cell-mediated immunity from the target cell surface? 3) What is the nature of the serum factor that augments the in vitro cell-mediated immune reaction? 4) Are target cell membrane antigens involved in immunological enhancement? 5) What is the role of macrophages in immunological enhancement? and 6) Is immunological enhancement another manifestation of antibody mediated suppression of the immune response?